A.V. misses the force of the imperfect, marking Peter's custom. Not only at church feasts, but at ordinary meals, in defiance of the Pharisaic that this prohibition was not binding (Act 10:28; Act 11:8, Act 11:9), and had defended that position in the apostolic conference (Act 15:7 ff.).
Withdrew and separated himself (ὑπέστελλεν καὶ ἀφώριζεν ἑαυτόν)
Or, began to withdraw, etc. Ὑποστέλλειν only here in Paul. It means, originally, to draw in or contract. Thus of furling sails, closing the fingers. Middle voice, to draw or shrink back from through fear. Hence, to dissemble or prevaricate. There seems to be no special reason for making it either a military metaphor, as Lightfoot, or a nautical metaphor, as Farrar. See on Act 20:20.